Reclaiming natural and synthetic rubber with bis (tetraalkylphenol) sulfides



United States Patent RECLAIMING NATURAL AND SYNTHETIC RUBBER WITHBIS(TETRAALKYLPHENOL) SULFIDES Wendell S. Cook, Houghton, Mich., andGeorge E. P. Smith, Jr., Akron, Ohio, assignors to The Firestone'Igrehtf; Rubber Company, Akron, Ohio, a corporation 0 O 'o No Drawing.Original application June 29, 1949, Serial No. 102,154, now Patent No.2,605,288, 29, 1952. Divided and this application August 2, Serial No.245,432

2 Claims. (Cl. 260-) This invention relates to the reclaiming ofvulcanized rubbery copolymer of styrene and l,3-butadiene, andvulcanized mixtures of such copolymer and natural rub- The vulcanizateswhich can be reclaimed according to the present invention are thevulcanizates which contain combined sulfur. They may be obtained byvulcanizing with sulfur, sulfur halides, polysulfides of phenols orcresols, dialkyl Xanthogen sulfides, tetraalkylthiuram sulfides or othersulfides known to vulcanize chemically unsaturated elastomers.Vulcanization may be effected with or without an accelerator. Theinvention includes new reclaiming agents as well as a process ofreclaiming.

Fundamental to a successful reclaiming operation is the reduction of avulcanizate to a plastic workable mass. In the case of vulcanizednatural rubber this may be accomplished by heat alone if maintained at atemperature substantially above that at which vulcanization occurred andfor a sufficient length of time. In addition, however, certain oils andresins which act as swelling agents, plas ticizers or tackifiers (e. g.,solvent naphthas, turpentine, dipentene, asphalt, pine tar, rosin,coumarone resins, rosin oil, etc.) are usually added to assist theprocess.

Also useful but to be distinguished from the oils and resins lastmentioned are certain chemicals which act catalytically to hasten thereclaiming process rather than 0 in a solvent or lubricating manner.Natural rubber has, for example, been reclaimed using such catalyticacting chemicals at temperatures as low as 150 F.

With the advent of GRS (butadiene-styrene copolymer) during World War IInew problems confronted the reclaimer. Vulcanizates of this substance donot behave as do those of natural rubber. Rather than having a softeningor plasticating effect, heat renders them harder and more unworkable.Large portions of oils of the solvent or lubricating variety werenecessary to produce a workable material. But due to the largequantities of oils used, the physical properties of the resultant material were very poor. Therefore, catalytic type reclaiming additives,which will be active in relatively small amounts and especially thoseeffective on synthetic rubber, become very important.

An object is to provide a method of reclaiming synthetic rubbers,particularly those of the butadienestyrene polymer type.

Another object is to provide reclaimed vulcanizates having improvedphysical properties.

. for vulcanized rubber and rubber-like compounds.

A still further object is to provide an improved method for thereclaiming of synthetic type rubbers.

The above and further objects will be manifest in the description of theinvention which follows.

It has been found that members of a new class of chemical compounds areeffective as reclaiming agents These chemicals are of particular valuein the reclaiming of type synthetic rubber and vulcanized mixturescontaining both natural rubber and GR-S. atively small proportions ofthe compounds are required. The new chemical compounds suitable forpractice of the invention are the tetraalkylphenol sulfides and arebelieved to have the following formula R1 OH OH R1 s Ra Ra wherein R1,R2, R3, and integer from 1 to 4 but or para to the OH group.

These tetraalkylphenol sulfides may be conveniently prepared by reactinga suitable tetraalkylphenol with sulfur chloride in an inert solventsuch as carbon tetrachloride or ethylene dichloride. The sulfideproduced with sulfur monochloride is preferred but products producedfrom all sulfur chlorides are active and are included in the invention.

Illustrative of the preparation of these materials 13 g. of2,3,5,6-tetramethylphenol was dissolved in 300 cc. of carbontetrachloride. Another solution was prepared by dissolving 5 g. ofsulfur dichloride in 10 cc. of carbon tetrachloride. The sulfur chloridesolution was added dropwise to the tetramethylphenol solution. Duringthe was recrystallized at 23 6 -23 7 obtained.

Percent cal- Percent culated for CzoHzaOzS found Sulfur 9. 70 9. 69

Other tetraalkylphenol sulfides of the invention may be prepared in themanner illustrated above by reacting a sulfur chloride with2,3,4-trimethyl-6-ethylphenol 3,4,5 ,G-tetramethylphenol2,3,5-trimethyl-o-isopropylphenol 2,6-di-tert-butyl-3,S-dimethylphenol2,3,4,6-tetramethylphenol 2,3,5,6-tetraethylphenol3,4,5,6-tetrabutylphenol 2,5-dimethyl-4,6-diisopropylphenol4-methyl-2,3,6-triethylphenol 2,3,4,6-tetrabutylphenol3-methyl-4,5,6-triethylphenol 3methyl-2,5,6-triisopropylphenolIndicative of value of a body, tack, and sheeting permits it to bestretched without tearing and having undue 1 surface irregularities.Tack is a quality of adhesiveness which is desirable in reclaimed rubberin that it facilitates fabrication of a composite article in which oneelement must be adhered to another before the article is vulcanized.

Since the two qualities last mentioned do not lend themselves well toinstrument evaluation, they are customarily determined by handestimation.

The body ratings used in establishing the merit of the present inventionwere estimated by observing the stretch or elongation of a refined sheetstretched by hand and by the appearance and uniformity of the stretchedsheet, and were recorded as good (G), fair (F), poor (P), tough (T), andlacey (L) or some combination thereof.

Tack was estimated by laying a portion of the refined reclaimed sheetacross the hand and then pressing the thumb and first finger together.When the thumb and first finger were spread apart, a small but definiteforce was required to separate the two adhering surfaces. A rating of 5was given to the force required to separate a sheet of typical naturalrubber whole tire reclaim. Milled crude rubber was given a rating of 10,and crude GR-S with no tack was given a rating of 0. (The higher thenumber the better the tack.) Values between these assigned controls wereestimated by the observer and could be duplicated easily by differentindependent observers with an accuracy of plus or minus one unit.

The facility of sheeting was noted by which roll the sheet adhered to oneach pass (Ffast roll, S-slow roll, N--neither roll). Best sheeting isreflected by adherence to the fast roll, poorest by adhering to neither.

A 200 gram batch of the following formula was mixed for ten minutes in aBaker-Perkins mixer.

Parts by weight Ground GR-S tread scrap (5 mesh) 100 Dipentene fractiona (B. P. l73-20l C.) 6 Coumarone indene resin b 62,3,5,6-tetraniethylphenol sulfide 1.5

Solvenol, supplied by Hercules Powder Company.

Cumar 2 MH, supplied by Barrett Division, Allied Chemical and DyeCorporation.

The mixed batch was then cooked for 4 hours in a pan heater at 175 p. s.i. steam pressure (377 F). The batch was then dried, cooled, mill-massedand subjected to three refining passes. Sheeting facility was recordedafter each pass. Thickness, body and tack were observed and recordedafter the third refining pass as follows Thickness inches 0.0075 Body FTack 3 Sheeting SPF The value of the tetraalkylphenol sulfides of thepresent invention becomes apparent by comparing the results obtainedabove, showing that the product of the invention is suitable for use asreclaimed rubber, with a run made in the absence of such sulfides butwith all other variables identical. A 200 gram batch of the followingformula was mixed for ten minutes in a Baker-Perkins mixer.

Parts by weight Ground GRS tread scrap (5 mesh) Dipentene fraction (B.P. l73-20l C.) 6.75 Coumarone indene resin 6.75

(It should be noted that the total weight of materials added to thescrap rubber here is the same as the total weight including thetetramethylphenol sulfide in the first nstance.) The mixed batch wasthen cooked for 4 hours in a pan heater at 175 p. s. i. steam pressure(377 F.). The batch was then dried, cooled, milled-massed and sub ectedto three refining passes. The observations and results were taken andrecorded as before with the following results.

Thickness inches 020 Body P-L Tack n 1- Sheeting SSF The product hereobtained, without benefit of the use of a tetraalkylphenol sulfide, wasof very inferior quality and could not be considered as reclaimed.

The lnvention is not limited to the specific conditions or quantitiesset forth herein. The temperatures set forth above, though preferred,are not critical and may Well be varied within a range of to 550 F.depending largely upon process and commercial considerations. Crudetetraalkylphenol sulfides are equally as elfective in reclaiming as arethe pure compounds. The amount of the sulfides required to produce thedesired results is not particularly critical and may well be varied from0.05 to 10 parts by weight for every 100 parts of vulcanized scrap.Other variations appearing naturally to those skilled in the art arewithin the contemplation of the present invention.

What is claimed is:

1. A process of reclaiming a vulcanized rubbery copolymer of styrene and1,3-butadiene which comprises heating the vulcanized copolymer at atemperature in the References Cited in the file of this patent UNITEDSTATES PATENTS 2,359,122 Kirby Se 1 2 2,495,145 Smith et al. Jim. 17

2,605,241 Albert July 29, 1952 OTHER REFERENCES Cook et al.: Ind. and EnCh 1194-1202. g em., July 1948, pages

1. A PROCESS OF RECLAIMING A VULCANIZED RUBBERY COPOLYMER OF STYRENE AND1,3-BUTADIENE WHICH COMPRISES HEATING THE VULCANIZED COPOLYMER AT ATEMPERATURE IN THE RANGE OF 150* F. TO 550* F. IN THE PRESENCE OF BIS(2,3,5,6TETRAMETHYLPHENOL) SULFIDE.